Because of the trend toward larger scale circuit integration and higher pin-count connectors, today's electronic circuits are increasingly characterized by lower electrical energy levels. Accordingly, mechanical energy rather than electrical energy must be relied upon to pierce the insulative surface films of the contact elements of connectors. A contact system ultimately derives its mechanical energy from a flexible contact element, like that found in a multi-finger clip, bearing against a mating element such as a post or pin typically having a square cross section.
As pointed out by Kantner and Hobgood in their paper, Hertz Stress as an Indicator of Connector Reliability, appearing in Connection Technology, March, 1989, pages 14-22, current flow in metallic electrical contacts is established through minute metal-to-metal contact sites formed as a result of Hertzian stress imposed on the contact element surfaces. The Hertzian stress (measured, for example, in psi) producing the contact sites is a function of not only the normal force applied by the contact elements by virtue of their spring properties, but also of the geometry of the contact elements and the modulus of elasticity of the contact material. For a given normal force, contact element geometries presenting smaller areas provide higher forces per unit area. Such higher stresses facilitate the mechanical penetration of surface films, resulting in the desired low and stable contact resistance. Accordingly, Hertzian stress, rather than normal force, is a key criterion indicative of contact performance, and higher Hertz stress connectors are to be preferred.
It is known that a highly reliable connector mating surface geometry is that which produces a "fine point" contact. Such a contact results, for example, from bringing together two rounded surfaces (sometimes referred to as a "crossed rod" contact configuration) and, not surprisingly, connectors employing such contact element geometries exhibit extremely high Hertzian stresses.
Accordingly, in the case of square connector posts or pins in which contact with mating elements is established through two opposing surfaces of the pin, it is desirable to fully round the opposing contact surfaces. However, existing fabrication processes impose certain limitations on the pin surface geometries that can be formed economically. For example, the mating contact surfaces of pins produced by existing punch press processes are not fully rounded. Instead, central flats remain on the opposed contacting surfaces of the pin which reduce Hertzian stresses and hence the reliability of the electrical connection afforded by the final product.
Thus, it is an overall object of the present invention to provide an electrical connector pin configured for high Hertzian stresses and low and stable contact resistance during use thereof.
It is a more specific object of the present invention to provide a connector pin having opposing contact or mating surfaces that are fully rounded.
It is yet another overall object of the present invention to provide a metal stamping process for fabricating connector pins that have opposed surfaces that are fully rounded.
Another object of the present invention is to provide an electrical connector pin that is a product of the aforementioned process.